Two scenarios, two answers

Scenario 1 — The Swiftvets put out an ad that questions whether John Kerry told the truth about his service during the Vietnam war. The charges go unaddressed for days. When they are finally addressed, the main argument is that the Bush campaign is behind the ads. Thus the charges remain largely unanswered.
Scenario 2 — CBS airs a story that questions whether George W. Bush told the truth about his service during the Vietnam war. In less than 24 hours, the main elements of the story (the things that made it different from past tellings) are pretty much discredited.
Question — How do we explain the difference betweeen these scenarios?
Answer 1 — The Swiftvet story is based on reliable evidence; the CBS story isn’t.
Answer 2 — The Democrats rely on an increasingly incompetent MSM; the Republicans don’t, and are the beneficiaries of the efforts of conservative bloggers and their readers.